Electrofluid converters

ABSTRACT

A converter or valve to modulate fluid flow, that includes a fluid channel to receive the fluid which is delivered to an output. An electrically-energized bender is disposed in close proximity to the output of the fluid channel; the bender is an elongate strip secured at one end and free to move at the other end toward or away from the output to interact with fluid flow from the output. An electric energy source is connected to bias the bender electrically to provide a small, controllable separation between the free end of the bender and the output of the fluid channel to provide an orifice for fluid flow, pumping action, as the bender moves relative to the output, upon a fluid film, separate from the fluid flow, serving either to compress or to expand the fluid film to achieve damping of the bender. The bender, in a modification, is shown in the form of a disc.

The present invention relates to apparatus operable interchangeably toconvert fluid pressure and electric signals.

Attention is called to a thesis entitled "A Proportional PiezoelectricElectro-Pneumatic Servovalve Design" (Herrick) and to a paper entitled"A Low Power Electro-Pneumatic Servovalve Design" (Taft and Burke, thepresent inventors), the latter being drawn upon heavily in thisspecification.

In most modern control systems a microprocessor is used as thecontroller. The microprocessor offers the benefits of rapid andcontinuous monitoring and processing of data and it provides as wellgreat flexibility in control strategy implementation. For amicroprocessor to be used in fluid systems of the type to which thisinvention is directed, there must be a compatible interface to couplethe microprocessor to the fluid system. A converter serving as suchinterface should be reliable and compatible with the digital to analog(D/A) output of the microprocessor; it is an object of the presentinvention to provide such a converter, an electropneumatic converterwhich, because of its high linearity and bandwidth and low powerconsumption, serves as a compatible and reliable interface between themicroprocessor and pneumatic control elements.

Another object is to provide a converter whose output can be electricalor can be mechanical.

Still another object is to provide a converter whose output signals,whether those signals be electrical or mechanical, are proportional(i.e., substantially linear) in the range of operation.

A further object is to provide a proportional device with low inputpower and high speed characteristics.

A still further object is to provide a device which produces an outputpressure proportional to an electrical signal with very low electricalpower input.

These and still further objects are addressed hereinafter.

The foregoing objects are achieved, generally, in a system or convertercomprising a plate or the like having a fluid-flow channel therein withan opening or port at one face thereof. A bender (or transducer) in theform of a sandwich of two piezoelectric strips or the like is secured,at one end thereof, to the plate, the free end of the strip beingdisposed over and in close proximity to the opening or port to form aflapper-nozzle, movement of the strip toward and away from the openingor port serving to affect fluid flow through the nozzle and, conversely,fluid flow through the nozzle serving to effect bending of the benderaway from and toward the opening or port. The bender, as later discussedin some detail, may be a disc secured at its periphery. Electric meansis connected to the bender to apply a bias voltage thereto, which biasvoltage is controlled to effect a small controllable separation betweenthe bender and the nozzle opening or port to provide an orifice forfluid passage. Pumping action of a fluid film between the bender and theplate is achieved whenever the bender moves relative to the plate toachieve damping of bender movement. A most important aspect of theinvention is a system or converter consisting of two benders in apush-pull configuration in which one bender, when actuated by anelectric potential, decreases fluid flow through one flapper-nozzle,while the other bender is actuated to increase fluid flow throughanother flapper-nozzle.

The invention is hereinafter described with reference to theaccompanying drawing in which:

FIG. 1 is a diagrammatic representation of a system embodying thepresent inventive concepts, that includes a fluid-control valve andassociated electrical circuitry;

FIG. 2 is a diagrammatic view showing the electrical control circuitryof FIG. 1 in greater detail and the two fluidcontrol valves as twofluid-control flapper-nozzles;

FIG. 3 is an elevation view, schematic in form and partly cutaway,showing the two fluid-control flapper-nozzles of FIG. 2 and relatedfluid mechanisms;

FIG. 4 is an isometric, exploded view of the two fluid-controlflapper-nozzles of FIG. 3 and related mechanisms;

FIG. 5 is an isometric, enlarged view showing in greater detail the twofluid-control flapper-nozzles of FIGS. 3 and 4;

FIG. 6 is an enlarged partial view taken on the line 6--6 in FIG. 5looking in the direction of the arrows;

FIG. 7 is a diagrammatic representation of a modification of a portionof the system of FIG. 1;

FIG. 8 is a plan view of a nozzle structure that differs structurallyfrom the two flapper-nozzles of FIG. 5; and

FIG. 9 is a representation taken on the line 9--9 in FIG. 8, looking inthe direction of the arrows, showing diagrammatically the nozzle of FIG.8 and immediately surrounding mechanical parts.

The system shown at 101 in FIG. 1 employs an electrofluid converter 106(that includes a fluid valve 102 and electrical circuitry 103) and alaminar proportional amplifier (LPA) 104 to drive a driven device 105.The converter 106 as a functioning unit, as indicated, includes both thevalve 102 and the electrical circuitry 103, as shown in greater detailin FIG. 2. The apparatus in FIG. 1 further includes an air supply inputat 1 from a fluid source 12 to both the fluid-control valve 102 and theLPA 104. The lines labeled 2 and 3 represent electrical conductors,whereas lines 1, 4 and 5 are fluid (e.g., air) lines. The conductor 3 isshown with arrows pointing in either direction to indicate thatelectrical signals can travel to the electrical circuitry 103 from theblock 102 as well as vice versa. As noted hereinafter, in operation as avalve, an electrical signal is applied to a piezoelectric bender ortransducer which controls fluid flow in a fashion proportional to themagnitude of the applied voltage and that is the mode of operationdiscussed in the first part of this explanation.

The fluid valve 102 is shown in FIG. 2 including two flapper-nozzles 6and 7 which are now explained with reference to FIGS. 3, 4, 5 and 6. Theflapper-nozzles 6 and 7 consist of benders 8 and 9, respectively, thatcontrol fluid flow into the chambers shown at 10 and 11, respectively,in FIG. 3 from fluid channels 15 and 16, respectively. The fluidemployed in the systems discussed herein is usually air and that fluidis emphasized here, but other fluids, including oil, may be employed.

Air passes into the lower port marked 1 in FIG. 3, thereafter flowing ina fluid line 13 or a fluid line 14 (formed in a plate 17B in FIG. 4; theplates 17A and 17B in FIG. 4 constitute the plate marked 17 in FIG. 3);the relative flows in 13 and 14 depend upon which of the nozzles 6 and 7is open wider. The term "open" herein is used to denote a condition inwhich air can flow upward from a channel 15 or 16, as the case may be,through the regions between the benders 8 and 9 and the plate 17A (inwhich the fluid channels 15 and 16 are formed), which regions serve ascontrolled orifices to emit fluid into the chambers 10 and 11 in a plate40 (which in actual apparatus are formed in a separate plate 40A, asshown in FIG. 4); the plate 40A plus plates 40B' and 40B" constitute theplate 40 in FIG. 3), as explained below in greater detail. The plates40B' and 40B" must be electrically insulated from one another (plate 40Ais an insulator), as do also the top surfaces of the benders 8 and 9that are connected to the plates 40B' and 40B" by the conductors 3A and3B, respectively, in FIG. 5.

Each of the benders 8 and 9, as shown in FIG. 5, is in the form of anelongate strip and each strip is piezoelectric. The benders 8 and 9 aresecured to the upper face marked 17A' of the plate 17 (FIG. 5) at ends8A and 9A thereof and are free at ends 8B and 9B to move toward and awayfrom the associated nozzle opening (i.e., in the y-direction in FIG. 6)respectively reducing and increasing air flow upward through the orificeformed between each output or opening of the fluid channels 15 and 16and the benders 8 and 9. Movement of the benders 8 and 9 is achieved byconnecting energizing voltages of opposite polarity across the twobenders 8 and 9, using the plate 17 and the conductors 3A and 3B. Theconductor 2A is an external connection necessary to complete the circuitbetween each bender and the electrical control circuitry 103 in FIG. 3.According to the present teachings the voltage applied to each benderincludes a low bias voltage (typically about +6 volts) which raises thebender to provide a gap d (˜0.001 inch) in FIG. 6 between the face 17A'of the plate and the bender. The bender (e.g., 8) can then move up (+y)or down (-y) in FIG. 6 respectively to cause an increase in flow and adecrease in flow through the orifice between the bender and the plate.According to the present teachings, the bender 8 is actuated to moveupward in FIG. 5 when the bender 9 is actuated to move downward. Theslight separation d of each bender from the plate allows the flowthrough the nozzles with zero input control signal to each bender to beadjusted by the resistors R₂ to balance them and also effects pumpingaction of fluid disposed between each bender and the plate whenever thebender moves relative to the plate to achieve damping of each bender.

As is indicated above, each bender is disposed within a cavity (i.e.,the cavities 10 and 11) having an exit port (i.e., the ports labeled 18and 19 formed in plates 40B' and 40B" in FIG. 4 and which together formthe output 4 in FIGS. 1 and 2) so that the bender acts as a variablerestrictor with respect to fluid movement into the associated cavity fora fixed pressure at the supply port 1. The ports 18 and 19 serve also ascontrol ports of the LPA (or fluidic amplifier): they are fixed in size;hence, fluid flow into the ports (and thus into the LPA) changes as therestriction changes. In accordance with the present teachings, thepush-pull activation of the bender 8 up and bender 9 down effects anincrease in fluid flow into the cavity 10 and a decrease flow into thecavity 11, thereby providing at the exit ports of the particular benderpair a differential pressure signal which is provided as input to theLPA (see the further explanation below).

The operation of the fluid valve 102 involves two energy conversions. Anelectrical signal is first converted to mechanical motion using apiezoelectric bender. The resulting mechanical motion is converted to apressure signal using the bender as a flapper-nozzle valve. Thepiezoelectric bender is a beam mounted in a cantilever fashion. Thebender consists of two sheets of lead zirconate titanate bonded onto acentral brass shim. The two sheets are coated with nickel to achievebetter distribution of electrical charges over the surface. When avoltage is applied to the bender, one of the two sheets of piezoelectricmaterial is placed in tension while the other is in compression; thusthe bender will deflect in a manner similar to a bimetallic strip. Theamount of deflection is on the order of thousandths of an inch and thecorresponding amount of output force that the beam produces is small. Tolimit the static and dynamic flow forces on the beam, small nozzlediameters of 0.030" (i.e., the cross-dimensions of the openings from thechannels 15 and 16 in FIG. 5) and low supply pressures (e.g., 0.0447psi) must be used in the nozzles 6 and 7 in FIG. 2. The resultingpressure signals downstream from the nozzles are also small; so somemechanism of pneumatic amplification must be used.

Amplification is accomplished by the laminar proportional amplifier 104in FIG. 1 which amplifies the pressure signal to some workable level.The LPA is a mechanism known to workers in this art. It is a no-movingpart pneumatic amplifier with high gain, high bandwidth and low noisecharacteristics. Several LPAs, usually, are cascaded and the block 104is considered to have one or more such units. The final pressure signalat 5 can be used to operate a pneumatic controller at 105 in FIG. 1 or asecond stage pneumatic power valve at 103. Although the LPA is a knowndevice, a short explanation of its operation is now made with referenceto FIG. 3.

The alternate fluid pressure signals that appear at 18 and 19 are usedas a differential pressure input to a first LPA such as the LPA showndiagrammatically and in detail in FIG. 3. A supply pressure ismaintained in a chamber 20 of the LPA in FIG. 3. This supply pressurecauses a laminar flow jet labeled 26 to flow through the channel labeled20A. This laminar flow jet passes through the rest of the device and issplit by a wedge 25. With no differential input, equal amounts of floware collected in two output ports 23 and 24. If the pressure at theinput port 19 is greater than the pressure at the other input port 18,the jet emitting from the channel 20A is deflected and more flow iscollected in the output port 23 (output 9A) than in the output port 24(output 9B). As a result of the larger fluid momentum in the port 23, apressure larger than the pressure in the port 24 is developed in theport 23. Only a small input pressure differential at 18 and 19 isrequired to deflect the jet 26 and this produces a larger outputpressure difference, thus resulting in a pressure gain. The outputpressure difference at 23 or 24, as the case may be, can be as much as0.7 of the supply pressure applied at 20. Chambers 21 and 22 are ventsto the atmosphere.

Another LPA could be placed in series with the first, using the outputsof the first LPA as inputs to the second. This would further amplify thepressure differential between the ports 18 and 19. In the present deviceemployed by the inventors, four amplifiers are cascaded in series toproduce a gain of 1650; it is considered, for present purposes and asabove noted, that the LPA 104 in FIG. 1 includes one or more suchamplifiers.

One form of electrical circuitry to achieve the present purposes isshown within the block 103 in FIG. 2, wherein the voltages at V aretypically +15 volts and -15 volts dc and the voltage at V' is a dcsignal with a maximum swing of ±6 volts. The circuit includes fixedresistors R₁, and potentiometers R₂ and R₃. The circuit also includesamplifiers 30 and 31 whose outputs apply voltages to the benders 8 and 9(see inputs 3A and 3B, respectively, in FIG. 5), the voltage applied tothe bender 8 (within the block 6 in FIG. 2) being connected through aninverter 32 to give the push-pull operation above discussed.

The information in this paragraph can be augmented by reference to theTaft et al. paper. The benders used in actual apparatus were strips thatmeasured 4.3×10⁻² m. long, 1.27× 10⁻² m, wide and 5.0×10⁻⁴ m. thick. Thevalve system was tested both statically and dynamically; it has anoverall sensitivity of 0.04 psi/volt and is linear around an operatingvoltage of ±6 volts with input pressure at 1 in FIG. 3 of 0.0447 psi;pressures in the chambers 10 and 11 depend on the position of respectivebender and were not measured.

The system in its present configuration has a system bandwidth of 500Hz. The electrical input power requirements to the valve 102 are verysmall due to the high input impedance (>20MΩ) of the piezoelectricbenders. The final output pressure signal has an amplitude of ±0.25 psi.

A most important aspect of the present invention is increased damping ofthe benders (or beams) 8 and 9 due to a film of air between each benderand the plate, which is squeezed or expanded as the bender moves. Thissqueeze-film damping is enhanced by mounting the bender nearly flushwith the surface of the plate 17 and serves, as is noted in some detailin the Taft et al. paper, greatly to reduce bender oscillations thatwould adversely affect the system 101 in FIG. 1.

Further, the converter 106 is a proportional device (i.e., linear) withlow power and high speed. Each bender deflects an amount proportional tothe magnitude of the voltage applied thereto and the downstream pressure(e.g., at 18 and 19) is proportional to the pressure in the chambers 10or 11. While the system described above provides an output pressuredifference proportional to the input voltage, it can be employed in atrue modulation sense in that the input air at 1 can be subjected tosmall modulations in the context of audible sound, for example, whichmodulations are converted by the bender to electrical signals or aflowmeter can be fabricated which will measure rate of change of such aflow. Such a flowmeter would be useful to measure pulsations in flow.

In the foregoing explanation, the benders discussed are piezoelectricstrips. The valve shown in FIGS. 8 and 9 employs a bender 8A in the formof a disc (it is intended that the term "disc" herein denotes a thinwafer whose cross-dimensions are usually circular but may take someother closed-loop shape). The disc 8A is secured at its periphery and isfree to move at its center toward and away from the output of a fluidchannel (which is again labeled 15 in FIG. 8) to interact with fluidflow from the output of the channel 15 and into a chamber 10A. Theoutput of the chamber 10A is again marked 18. A small spacing labeled din FIG. 9 between the bender 8A and a flat surface formed in the platemarked 17C (in which the chamber 10A is formed), serves the dampingfunction above discussed. The valve of FIGS. 8 and 9 may have a feedbackinput at 5C in FIG. 9 from the LPA 104 in FIG. 7 to further assist indamping and other effects on the bender 8A.

Modifications of the invention herein disclosed will occur to personsskilled in the art and all such modifications are deemed to be withinthe scope of the invention as defined by the appended claims.

What is claimed is:
 1. A converter for modulating fluid flow, thatcomprises:a plurality of piezoelectric benders, each in the form of anelongate strip; an equal plurality of fluid-flow channels, onefluid-flow channel being associated with each bender of the plurality ofbenders and being formed in a flat plate with the channel output openingat the face of the plate; each bender being secured to the face of theplate at one end and being free to move toward and away from theassociated channel output opening at the other end thereof to form aflapper-nozzle which serves to control fluid flow from the outputopening; and electric means connected to each of the benders to apply abias voltage thereto to alter the zero-signal position of each saidflapper-nozzle and to balance the zero-signal position of each saidflapper-nozzle, said electric means being further connected to apply anactuation voltage to the benders to effect deflection thereof away fromsaid zero-signal position, a bender, upon application of said actuationvoltage, being deflected toward the associated output opening to cause adecrease in fluid flow from the associated output opening while anotherbender is deflected away from the associated output opening to cause anincrease in fluid flow from the associated output opening.
 2. Aconverter as claimed in claim 1 comprising two benders, each bender,when electrically biased, being only slightly separated from the plate,so that subsequent bender motion will effect pumping action of fluiddisposed between each bender and the plate whenever the bender movesrelative to the plate to achieve damping of each bender.
 3. A converteras claimed in claim 2 wherein each bender is disposed within a cavityhaving an exit port so that the bender acts as a variable restrictorwith respect to fluid movement into the cavity from said output openingfor a given pressure difference between the exit port of the cavity andthe associated nozzle input.
 4. A system comprising a converter asdefined by claim 3, that further includes amplifier means to receive asinput thereto the two outputs from the converter exit ports and operableto amplify any differences between the fluid pressures of the twooutputs.
 5. A converter as claimed in claim 2 comprising two fluidoutputs, one associated with each bender, such that, for a given fixedinput of fluid to the flapper-nozzles, the output pressure of oneflapper-nozzle will fall for a given applied voltage and the output ofthe other flapper-nozzle will rise.
 6. A converter as claimed in claim 1wherein said plurality of benders and associated openings comprise aplurality of bender pairs and associated opening pairs, each benderhaving an exit port therefrom, electric means to apply a voltage to eachbender such that one bender of each pair, upon application of thevoltage, moves toward the plate while the other bender of the same pairmoves away from the plate to provide at the exit ports of the particularpair a differential pressure signal.
 7. A system that includes aconverter as defined by claim 6 that further includes amplifier means toreceive the differential pressure signal and operable to amplify thesame.
 8. A converter that comprises:a plate having a fluid-flow channelthrough the thickness dimension thereof and having an output port at theplate surface; a piezoelectric bender in the form of an elongate strip,one end of the bender being secured to the plate and the other, freeend, being disposed over the output port of the fluid-flow channel toform a flapper-nozzle so that fluid flow through the nozzle effectsbending of the bender away from and toward the output port, fluid-flowaway from the output port effecting bending of the bender away from theoutput port; and electric means connected to the bender to apply a biasvoltage thereto, which bias voltage is controlled to effect a smallseparation between the bender and the channel output port to provide anorifice for said fluid flow, a fluid film, separate from said fluidflow, being compressed or expanded whenever the bender moves relative tothe plate to achieve damping of bender movement, in which said fluidflow is modulated and in which the modulations are converted by thebender to electrical signals.
 9. A dynamic flowmeter comprising theconverter of claim 8 and further including means connected to receivethe bender voltage produced by bender deflection and to sense changestherein, which changes occur because of a piezoelectric-generatedvoltage occasioned by bending of the bender due to changes in the flowof the fluid through the orifice.
 10. For use in a converter thatfurther includes electric means, a fluid valve that comprises twoelectrically energized benders; two fluid-flow channels, one channelbeing associated with each bender, each channel having an outputopening; each said bender at one end thereof being secured in fixedspaced relationship to the associated output opening, the free end ofeach bender being disposed to cover the associated output opening tointeract with fluid flow emitting from the associated output opening.11. A converter that includes the fluid valve of claim 10 and thatfurther includes electric means connected to energize the benders tobias the respective bender to effect a small separation between eachbender and the associated opening to provide an orifice for fluidpassage which achieves pumping action whenever the bender moves relativeto the plate to achieve damping of bender movement.
 12. A converter formodulating fluid-flow, that comprises:a. a plurality of piezoelectricbenders, each bender in the form of an elongate strip; b. a plate havinga plurality of chambers, one chamber being associated with each benderof the plurality of benders, said chamber comprising:i. a cavity withinwhich said associated bender is disposed, and where said fluid ismodulated, ii. a channel (or input port) supplying a nonmodulated fluidto said cavity with said associated bender, and iii. an exit (or outputport) extending from said cavity with said associated bender to conductsaid modulated fluid away from said cavity and said associated bender;c. means for connecting one end of each bender strip to the surface ofsaid cavity in cantilever fashion, the other end of said bender stripbeing free to deflect toward and away from said channel associated withsaid cavity, in order to modulate fluid-flow from said channel; and d.electric means connected to said bender to apply a bias voltage to eachbender, said electric means being further connected to apply anactuation voltage to each bender to effect deflection thereof, a benderupon application of said actuation voltage, being deflected toward theassociated opening to effect a decrease in fluid flow through theopening while another bender is deflected away from the associatedopening to permit an increase in flow of fluid through the opening.